1. Field of the Invention
The invention relates to a cable bushing for a measuring probe.
2. Background Discussion
Measuring probes, for example pressure measuring probes, are frequently used by introducing them into a container on a cable for example. The cable is used here to form an electrical connection to the measuring probe and for its mechanical attachment. Particularly suitable for this are cables which have on the outside a metallic shield which is surrounded example, by a plastic. The supply lines andlor signaling lines can then lead in the interior of the shield, protected against external influences to the probe.
The cable leads from the probe out of the container to a superordinate unit, for example a power supply and/or further electronics.
One application is the filling level measurement using a pressure measuring probe. Here, the pressure measuring probe is introduced on the cable into a container filled with a material. The pressure determined by the pressure measuring probe corresponds to the height of the material above the pressure measuring probe and is therefore a measure of the filling level in the container.
In these applications, in order to provide a seal, for example to ensure that no material escapes or penetrates downstream electronics and/or a superordinate unit, a cable bushing is necessary which has a housing through which the cable is led. The housing can be part of the superordinate unit here and/or also part of an attachment device for the probe, by virtue of the fact that the housing is mounted at the measuring location , for example on a container, by means, for example, of a flange or a thread.
The cable bushing can equally be arranged on the probe and connected, for example, to the probe or a probe housing, and ensure that no substance penetrates the probe.
An object of the invention is to provide a cable bushing for a probe which is as small, simple and cost-effective as possible.
For this purpose, the invention consists in a cable bushing for a probe having
a cable,
a housing,
through which the cable is led, and
which has, at a first end, a step which extends
radially inward,
a first sleeve,
which engages around the cable and
which has a first section arranged inside the housing, the first sleeve bearing against the cable in a seal-forming fashion, and
a sealing means being provided between the step in the housing and the first sleeve,
a second sleeve, which is arranged inside the housing,
which has a first cylindrical section which engages closely around the cable,
which has a second section which adjoins an end of the first section which faces the step, which bears on the first section of the first sleeve, and
an attachment element,
by means of which the second sleeve is pressed against the first sleeve.
According to one embodiment, the attachment element is a ring nut screwed into the housing in the direction facing the step.
According to another embodiment, the second sleeve is metallic and is pressed with the cable in order to provide strain relief to the cable.
According to a further embodiment, the cable is surrounded on the outside by a metallic shield, the second sleeve is metallic and the second sleeve forms an electrically conductive connection between the housing and the metallic shield.
According to yet another embodiment, the first sleeve is composed of a plastic, the cable has a coating made of a plastic and the first sleeve is welded to the coating.
According to a first preferred embodiment, the step in the housing is a radially inwardly extending shoulder, and the sealing means is a seal which bears on the shoulder, which is clamped in between the shoulder and the first section of the first sleeve.
According to a second preferred embodiment, the step in the housing is a radially inwardly extending shoulder, and the sealing means is provided by means of an inner edge of the shoulder onto which the first section of the first sleeve is pressed by means of the attachment element.
According to another embodiment, a spring is clamped in by means of the attachment element and exerts on the first sleeve a force in the direction facing the step.
According to yet a further embodiment of the development, the spring bears on an annular plate which bears on the first sleeve.
According to a third preferred embodiment, the step in the housing has a conical inner casing surface whose diameter decreases in the direction of the first end of the housing, the first sleeve is composed of an elastomer, the first section of the first sleeve has a conical region, and the first sleeve is pressed against the step in the housing by the attachment element in such a way that the conical region of the first sleeve presses against the conical casing surface of the housing and the first housing bears in a seal-forming fashion against the housing and the cable.
According to a particular embodiment,
the housing has a first part which comprises the first end of the housing, and a second part,
the second part is screwed onto the first part in the direction facing the step,
the attachment element is a radially inwardly extending step arranged in the interior of the second part,
which bears on the second sleeve and
which presses the second sleeve in the direction facing the step as a result of the second part being screwed on.
One advantage of the invention consists in the fact that the cable bushing has a very small number of small-dimensioned components.
A further advantage consists in the fact that in the cable bushing according to the invention, not only is there a strain relief for the cable but also at the same time the shield is connected to ground or to a reference potential via the housing.
The invention and its advantages will now be explained in more detail with reference to the figures in the drawing in which four exemplary embodiments are illustrated; identical elements are provided with the same reference symbols in the figures.